50GHz gallium arsenide electro-optic modulators for spaceborne telecommunications

Travelling-wave electro-optic modulators designed for V-band space applications using gallium arsenide guided-wave technology are presented. The designs feature a low-loss folded optical configuration giving straight-line RF access at one end of the chip, with all optical I/O via the opposite end. This configuration enables the close-packed monolithic modulator arrays needed for phased-array applications, contributes to high modulation bandwidths with low ripple by eliminating directional change in the RF feed arrangements and facilitates compact packaging. While only 1550nm designs are reported here, the AlGaAs material system is versatile, permitting modulators to be realized for a wide range of optical wavelengths, with particular advantage in drive-power at shorter wavelengths. Both single MZ and monolithic dualparallel (IQ) modulators have been assessed up to 70GHz; bandwidths around 50GHz are achieved with low-frequency Vπ of 4.6V. Typically, the folded devices are half the length of conventional format modulators and can accommodate 4 device arrays in the same width package.